For the brownie base:
- 3/4 cup flour
- 1/2 teaspoon salt
- 1 tablespoon cocoa powder
- 5 ounces dark or bittersweet chocolate (60-72%), chopped, or use chips
- 1/2 cup butter (1 stick)
- 3/4 cup sugar
- 1/4 cup brown sugar, firmly packed
- 3 eggs
- 1 teaspoon vanilla
For the buttercream layer:
- 3/4 cup sugar
- 2 tablespoons flour
- 3/4 cup milk
- 3-4 tablespoons heavy cream, divided
- 1 1/2 sticks butter (3/4 cup), softened but still cool, cut into cubes
- 1 teaspoon peppermint extract
- Green food coloring (optional)
For the chocolate glaze:
- 6 ounces dark or bittersweet chocolate (60-72%), chopped, or use chips
- 1 teaspoon light corn syrup
- 1/2 cup (1 stick) butter
Make the brownie base:
Pre-heat the oven to 325°F. Spray the sides and bottom of a glass or light-colored metal 9-inch x 13-inch pan with nonstick cooking spray. Line the bottom with parchment paper and spray the paper.
In a medium size bowl, whisk together the flour, salt and cocoa powder. Melt the chocolate and butter in the microwave in a medium size bowl, stirring frequently to avoid scorching. When melted and smooth, immediately add both sugars and whisk until completely combined. Let cool to room temperature and mix in the eggs until just combined. Do not overmix or the brownies will be too cakey. Add the vanilla and stir until just combined. Sprinkle the flour mixture over the batter and fold in the ingredients with a rubber spatula until just combined.
Pour the batter into the prepared pan and bake for 12-15 minutes, rotating the pan halfway through baking time. A toothpick inserted in the middle should have a few moist crumbs attached. Let the brownies cool completely.
Make the buttercream layer:
In a medium size heavy-bottomed sauce pan, whisk the sugar and flour together. Add the milk and 3 tablespoons of the cream and cook over medium heat, whisking occasionally, until the mixture comes to a boil and has thickened, 5-7 minutes. Remove the mixture from the heat and beat with an electric mixer on high until cool. Reduce the speed to low and add the butter. Mix until thoroughly incorporated. Increase the speed to medium-high and beat until the filling is light and fluffy. Add the peppermint extract and green food coloring, if using (add until you get the desired green tint you're looking for), and beat until combined. The consistency should be smooth and creamy. If too stiff, add the additional tablespoon of cream. Spread the buttercream over the cooled brownie layer and chill in the refrigerator for at least 45 minutes.
Make the chocolate glaze:
In a medium size bowl, combine the chocolate, corn syrup and butter and melt in the microwave, stirring with a rubber spatula and checking often to avoid scorching. When melted, stir vigorously for 1 minute to cool. Pour over the buttercream layer, tipping pan in each direction so the buttercrream is completely and evenly covered with the glaze. Chill the bars in the fridge for at least 1 hour.
When ready to serve, remove the pan from the fridge 15 minutes prior and cut the bars into squares with a warm knife and serve immediately. Store in the refrigerator for up to four days.